1. Field of the Invention
This invention relates to a compliant guide for accessing seabed installations such as sea-based oil or gas wells, systems using the guides, methods for dispensing coiled tubing with the compliant guide to such installation and methods for making and using same.
More particularly, this invention relates to a system for accessing seabed installations including a compliant guide for coiled tubing, flexible shafts or other similar apparatus. The compliant guide attaches at its first end to an injector apparatus and at its second end to a seabed installation providing a guide conduit for coiled tubing or other apparatus to feed same to the seabed installation. This invention also relates to methods for making the guide and systems and methods for using the guide and system.
2. Description of the Related Art
When inserted into an oil well, coiled tubing has a wide variety of uses such as drilling, logging and production enhancement according to known art. Coiled tubing can be withdrawn from a well immediately following a well treatment, or it can be permanently left in the well as part of the well completion. When coiled tubing is used, it is necessary to provide an annular well seal where the coil tubing enters the well. This seal is sometimes referred to as the xe2x80x9cstuffing boxxe2x80x9d or xe2x80x9cstripperxe2x80x9d, and its function is to provide a dynamic, pressure tight seal around the coiled tubing to prevent leakage of the well fluids from the oil well at the point where the coiled tubing enters the oil well. Prior art methods and apparatus have positioned the annular well seal close to the injector, typically only a few inches away, for the primary purpose of avoiding buckling failure of the coiled tubing between the injector and the annular well seal.
According to the prior art, oil wells on land require a lubricator. This is a device that can be many tens of feet tall and is temporarily attached to the wellhead or tree of the well. The injector must be held in place above this lubricator, close to the annular well seal. Substantial cranage or support structure is required to lift and hold the injector in place. Providing such cranage or structures adds to the cost, complexity, and duration of coiled tubing operations.
According to the prior art, underwater oil wells with surface wellheads are similar to land oil wells in that they require that the injector be lifted and held in place above the lubricator and close to the annular well seal. An additional disadvantage is that the injector must be lifted from a floating vessel onto the facility that has the surface wellheads. Many off-shore platforms do not have installed cranes adequate for this task, and the cost of temporarily providing such cranes may preclude the economical use of coiled tubing altogether.
According to the prior art, coiled tubing may be used in the case of underwater oil wells with temporary surface wellheads. In some instances a drilling vessel is connected to the underwater oil well with a temporary riser. This would occur during the drilling phase of an underwater oil well. A lubricator is sometimes attached to the temporary surface wellhead, and in such instances the injector must be transferred from a floating vessel, lifted and held above the lubricator close to the annular well seal. Since the drilling vessel floats freely without mooring, the injector must be heave compensated.
Underwater oil wells, with subsea wellheads which do not have any type of platform structure on the surface above the well, are generally accessed from a drill ship or semi-submersible drilling type vessel. According to the prior art, coiled tubing access from such vessels requires that the pressurized well bore to be temporarily extended by use of a tensioned rigid riser from the wellhead to the vessel and associated large heave compensation and riser handling equipment. This then allows the annular well seal to be close to the injector. Examplary of such prior art are U.S. Pat. No. 4,423,983 which discloses a fixed or rigid marine riser extending from a subsea facility to a floating structure located substantially directly above; and U.S. Pat. No. 4,470,722 which discloses a marine production riser for use between a subsea facility (production manifold, wellhead, etc.) and a semi-submersible production vessel. Other related prior art includes U.S. Pat. No. 4,176,986 which discloses a rigid marine drilling riser with variable buoyancy cans. Drill ships or semi-submersible drilling type vessels and associated equipment required for tensioned rigid risers have a high daily cost. For example, routine coiled tubing access performed on a subsea well may have a substantial daily cost in excess of one hundred thousand dollars per day.
In an effort to preclude the need for tensioned rigid risers and riser heave compensation systems, prior art that uses flexible risers in place of rigid risers has been disclosed. Examplary of such prior art are U.S. Pat. No. 4,556,340 and U.S. Pat. No. 4,570,716 that disclose the use of flexible risers or conduits between a subsea facility and a floating production facility; and U.S. Pat. No. 4,281,716 that discloses a flexible riser to facilitate vertical access to a subsea well to perform wireline maintenance. Other related prior art includes U.S. Pat. No. 4,730,677 that discloses a method and system for servicing subsea wells with a flexible riser and U.S. Pat. No. 5,671,811 that discloses a tube assembly for servicing a subsea wellhead by injecting an inner continuous coiled tubing into an outer continuous coiled tubing. What this prior art has in common is the extension of the pressurised well bore from the wellhead to the floating facility to allow the annular well seal, for either wireline or coiled tubing, to be above the water surface or close to the injector.
Damage, failure or emergency disconnection of a riser connected between a subsea wellhead and a floating vessel, or of tubing between a facility with surface wellheads and a floating vessel, can create safety hazards and a pollution risk if there are pressurised well fluids inside the riser or tubing. These risk factors are of significant concern and are often cited as the reason for not carrying out a particular oilfield operation. These concerns are heightened if the floating vessel is maintained in position by means of dynamic positioning instead of anchors. Such a vessel can accidentally move off station and reach the geometric or structural limit of the riser very quickly, within a few tens of seconds, depending on the water depth. Concerns about fatigue failure also arise if this riser or tubing is a homogeneous steel structure that is subjected to both pressure and varying stresses due to the relative motion between the wellhead and floating vessel and due to environmental forces.
Prior art methods and systems for accessing subsea wells with wireline exist which do not use risers to temporarily extend a pressurised well bore up to a floating vessel. Instead, a subsea lubricator may be used which connects directly onto a subsea tree or wellhead. A subsea lubricator is a free standing structure on a subsea tree. It is generally 50 ft. to 100 ft. tall with an annular well seal at the top that allows a wireline to enter from ambient pressure into a lubricator that is at well pressure. The top of a subsea lubricator remains underwater at a sufficient depth to allow for at least the draft of a floating support vessel which holds a wireline winch and ancillary support equipment. Subsea lubricators can be dispatched from vessels that are not drill ships or semi-submersible drilling type vessels and thus provide the flexibility to use vessels with a lower daily cost and other advantageous attributes such as rapid mobilization time offered by dynamically positioned vessels. Exemplary of this prior art are U.S. Pat. No. 4,993,492 that discloses a method of inserting wireline equipment into a subsea well using a subsea wireline lubricator; and U.S. Pat. No. 4,825,953 that discloses a wireline well servicing system for underwater wells using a subsea lubricator. The range of tasks that can be accomplished in a well by use of wireline alone is greatly increased by using coiled tubing together with wireline.
One prior art method disclosed in U.S. Pat. No. 4,899,823 holds the injector in place above a subsea lubricator that is connected to a subsea wellhead. The injector is positioned underwater to place it in close proximity to the annular well seal. A disadvantage of this approach is that since the injector is large and heavy, only relatively short subsea lubricators can be used. Otherwise, excessive bending moments can be applied to the subsea wellhead in the event of waves, currents or other forces acting on the injector. A relatively short lubricator limits the scope of downhole coiled tubing operations to ones that can be accomplished with only relatively short toolstrings.
Thus, it would represent an advancement in the art to provide a system for inserting coiled tubing into an oil well using an injector that is remote from the annular well seal. Providing an apparatus that increases the distance between the injector and the annular well seal from a few inches to up to hundreds or thousands of feet makes possible a range of new methods and systems for inserting coiled tubing, into a variety of oil wells, which were either too risky or impractical up to now. Oil wells on land, underwater oil wells with subsea wellheads, underwater oil wells with surface wellheads, oil wells on offshore platforms and oil wells still in the drilling phase can all benefit from the apparatus, methods and systems having remote coiled tubing injector capabilities.
The present invention provides a system designed to substantially increase the distance between an injector for coiled tubing or similar flexible material or apparatus and an oil well or other similar installation. In the case of pressurized installations such as an oil or gas well on the seabed, the system of the present invention can include a pressure seal associated with a distal end of the apparatus, while in the case of installations where the well bore is extended using a production riser to a site remote from the seabed such as the surface, the apparatus can include a pressure seal at the point of entry into the riser.
The present invention includes a spoolable compliant guide (sometimes xe2x80x9cSCGxe2x80x9d) comprising a hollow, continuous or jointed tube having a first end for detachably engaging an installation and a second end for detactably engaging an installation servicing apparatus.
Preferably the SCG is capable of withstanding tension and compression forces in excess of about 50,000 lbs. and spoolable onto a reel for ease of transport and speed of deployment and recovery.
The SCG is sufficiently long to assume a compliant shape between an injector and an installation such as a lubricator attached to a undersea wellhead. The compliant shape facilitates dynamic bending enabling relative movement between the injector and lubricator and avoiding the need for heave compensation of either the SCG itself or the injector. A desired compliant shape can be obtained through the use of bend restrictors, buoyant members, weights and/or ballasting members attached to the SCG and positioned along its length. Because the SCG can dynamically bend, vessels incorporating riser tensioning and heave compensation systems are not required for subsea wellhead operations.
The SCG can be provided with an internal anti-friction device to reduce or minimize tension and compression of the coiled tubing between the injector and the annular well seal.
The SCG can also include an emergency disconnect and a coiled tubing cutter between the annular well seal and the injector so that the SCG with the coiled tubing therein can be relatively instantly disconnected from the lubricator leaving the annular well seal connected to the lubricator.
If desired, the annulus between the coiled tubing and the SCG can be filled with a pressurized lubricating medium by incorporating a second annular seal at the injector end of the spoolable compliant SCG.
The SCG also includes an annular seal against well pressure and well fluids at the lubricator end and does not have well fluids inside thereby reducing or minimizing the consequences of failure or damage compared to tubing which does contain pressurized well fluids. Therefore, the SCG can be used without regard to the containment of pressure or well fluids. Because the annular well seal of the SCG is at the lubricator, a subsea lubricator system can be used for accessing subsea wells with coiled tubing while the injector remains on the floating vessel.
The SCG can also include an outer and inner tube with an annular space there between and orifices for circulating a fluid through the annular space. The SCG can also include dynamic force sensors coupled to dynamic force compensation apparatus positioned along the length of the SCG for countering lateral forces (i.e., applying an equal and opposite force at a selected position or positions) when the SCG is connected to the installation. The SCG can also include dynamic force sensors positioned along the length of the SCG, but especially at the wellhead end of the SCG, coupled to a dynamic repositioning apparatus associated with a vessel for countering lateral forces acting on the well head (i.e., moving the vessel so as to apply an equal and opposite force) when the SCG is connected to the installation.
The present invention also provides a system including an SCG, coiled tubing or similar apparatus, a lubricator and an injector facility including an injector, a guide spool, a coiled tubing spool and associated equipment to operate the injector and spools. The system facilitates vertical access to a deep oil well and insertion of the coiled tubing or a similar material or apparatus therein to. The system may include a blowout preventer, lubricator section, wellhead connector and a guide connector for attaching to the SCG. One end of a the SCG apparatus is detachably connected to a lubricator guide connector and the other end is detachably connected to the injector facility, near to an injector. The injector facility can be a vehicle, a floating vessel, a drilling rig or other suitable facility.
The system can also include a coiled tubing tool which can be connected to an end of the coiled tubing as it emerges from the lubricator end of the SCG, but prior to the SCG""s attachment to the lubricator. Alternatively, if the internal diameter and curvature of the SCG allows, then the coiled tubing tool can also be connected to the coiled tubing prior to insertion into the SCG. The toolstring (coiled tubing tool and coiled tubing) is designed to enter the lubricator prior to the SCG""s being detachably connected to the lubricator.
The present invention further includes a method for accessing an installation with a compliant SCG, where the method includes detachably connecting one end of a SCG to the installation and the other end of the SCG to a distant facility. A flexible apparatus can then be fed through the SCG into the installation. Finally, the method includes detaching the SCG.
The present invention further includes a method for inserting coiled tubing or other flexible continuous or jointed conduit or apparatus into a wellhead, where the method includes attaching a lubricator to a wellhead; detachably connecting one end of a SCG to the lubricator and the other end to an injector facility. The injector facility may include an injector, a guide spool, a coiled tubing spool and associated control apparatus. The coiled tubing is then introduced into the SCG by means of the injector""s unreeling the tubing from its storage reel or spool, urging the coiled tubing through the injector and then into and through the SCG. The method may include connecting a coiled tubing tool to the coiled tubing once it has emerged from the lubricator end of the SCG and before the SCG is attached to the lubricator. Alternatively, if the internal diameter and curvature of the SCG allows, then the coiled tubing tool can be connected to the coiled tubing prior to insertion into the SCG. The coiled tubing with the tool connected thereto (the toolstring) is then introduced directly into the lubricator. The toolstring is then inserted into the oil well through the injector. The above processes can be reversed to retrieve all of the items from the oil well.
The present invention also provides an SCG for guiding coiled tubing into a riser comprising a hollow, continuous or jointed tube having a first end detachably connected to a riser for an installation such as an oil or gas well and a second end for detachably engageable with an installation servicing apparatus. Preferably, the SCG is capable of withstanding tension and compression forces in excess of about 50,000 lbs. and spoolable onto a reel for ease of transport and speed of deployment and recovery.
The present invention also provides a coiled tubing system for use with risers. This system comprises a string of coiled tubing, a coiled tubing injector cooperable with a well bore seal and an SCG, a hollow, continuous or jointed tube including a first end having an optional connector for detachably engaging an installation such as an oil or gas well located at a proximal end of a riser and a second end for detachably engaging the injector. The SCG with the coiled tubing inside extends from a proximal end of the riser to the wellhead at the distal end of the riser. This system is especially well-suited for risers made of unbonded flexible pipe, where the SCG is reactively coupled to the coiled tubing. Because the SCG is reactive with the coiled tubing, the SCG accommodates the compressive forces associated with coiled tube operations, especially extraction, without damage to the unbonded flexible pipe.
The present invention also provides methods for performing coiled tubing operations through a riser, especially an unbonded flexible riser, without damage to the riser due to compressive forces that are generally encountered during coiled tubing extraction. The method includes inserting coiled tubing into an SCG of the present invention, inserting the combined structure through a proximal or surface end of the riser until a working end of the coiled tubing contacts the wellhead, injecting the combined structure into the wellhead and removing the combined structure from the riser upon completion of a coiled tubing operation.